==================================================================
BUG: KASAN: use-after-free in disk_unblock_events+0x4b/0x50 block/genhd.c:1644
Read of size 8 at addr ffff88809a001cc8 by task syz-executor.5/9045

CPU: 0 PID: 9045 Comm: syz-executor.5 Not tainted 4.14.182-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:17 [inline]
 dump_stack+0x1b2/0x283 lib/dump_stack.c:58
 print_address_description.cold+0x54/0x1dc mm/kasan/report.c:252
 kasan_report_error mm/kasan/report.c:351 [inline]
 kasan_report mm/kasan/report.c:409 [inline]
 kasan_report.cold+0xa9/0x2b9 mm/kasan/report.c:393
 disk_unblock_events+0x4b/0x50 block/genhd.c:1644
 __blkdev_get+0x79c/0x10c0 fs/block_dev.c:1556
 blkdev_get+0x84/0x8a0 fs/block_dev.c:1612
 blkdev_open+0x1cc/0x250 fs/block_dev.c:1770
 do_dentry_open+0x44b/0xec0 fs/open.c:777
 vfs_open+0x105/0x220 fs/open.c:888
 do_last fs/namei.c:3428 [inline]
 path_openat+0xb68/0x2aa0 fs/namei.c:3569
 do_filp_open+0x18e/0x250 fs/namei.c:3603
 do_sys_open+0x292/0x3e0 fs/open.c:1081
 do_syscall_64+0x1d5/0x640 arch/x86/entry/common.c:292
 entry_SYSCALL_64_after_hwframe+0x46/0xbb
RIP: 0033:0x45ca69
RSP: 002b:00007f6d098eac78 EFLAGS: 00000246 ORIG_RAX: 0000000000000101
RAX: ffffffffffffffda RBX: 00000000004f7a00 RCX: 000000000045ca69
RDX: 0000000000000000 RSI: 0000000020000080 RDI: ffffffffffffff9c
RBP: 000000000078bf00 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
R13: 00000000000007ae R14: 00000000004ca83b R15: 00007f6d098eb6d4

Allocated by task 1:
 save_stack mm/kasan/kasan.c:447 [inline]
 set_track mm/kasan/kasan.c:459 [inline]
 kasan_kmalloc.part.0+0x4f/0xd0 mm/kasan/kasan.c:551
 kmem_cache_alloc_node_trace+0x153/0x400 mm/slab.c:3661
 kmalloc_node include/linux/slab.h:526 [inline]
 kzalloc_node include/linux/slab.h:672 [inline]
 alloc_disk_node+0x5d/0x3d0 block/genhd.c:1387
 md_alloc+0x20e/0x810 drivers/md/md.c:5322
 md_probe+0x28/0x40 drivers/md/md.c:5379
 kobj_lookup+0x221/0x410 drivers/base/map.c:124
 get_gendisk+0x36/0x240 block/genhd.c:785
 __blkdev_get+0x3e5/0x10c0 fs/block_dev.c:1451
 blkdev_get+0x84/0x8a0 fs/block_dev.c:1612
 blkdev_open+0x1cc/0x250 fs/block_dev.c:1770
 do_dentry_open+0x44b/0xec0 fs/open.c:777
 vfs_open+0x105/0x220 fs/open.c:888
 do_last fs/namei.c:3428 [inline]
 path_openat+0xb68/0x2aa0 fs/namei.c:3569
 do_filp_open+0x18e/0x250 fs/namei.c:3603
 do_sys_open+0x292/0x3e0 fs/open.c:1081
 autodetect_raid init/do_mounts_md.c:297 [inline]
 md_run_setup+0x76/0xa7 init/do_mounts_md.c:311
 prepare_namespace+0x42/0x212 init/do_mounts.c:567
 kernel_init_freeable+0x5f8/0x615 init/main.c:1093
 kernel_init+0xd/0x15b init/main.c:1000
 ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:404

Freed by task 9045:
 save_stack mm/kasan/kasan.c:447 [inline]
 set_track mm/kasan/kasan.c:459 [inline]
 kasan_slab_free+0xaf/0x190 mm/kasan/kasan.c:524
 __cache_free mm/slab.c:3496 [inline]
 kfree+0xcb/0x260 mm/slab.c:3815
 device_release+0xf0/0x1a0 drivers/base/core.c:831
 kobject_cleanup lib/kobject.c:646 [inline]
 kobject_release lib/kobject.c:675 [inline]
 kref_put include/linux/kref.h:70 [inline]
 kobject_put+0x13e/0x1f0 lib/kobject.c:692
 put_disk+0x1f/0x30 block/genhd.c:1452
 __blkdev_get+0x707/0x10c0 fs/block_dev.c:1549
 blkdev_get+0x84/0x8a0 fs/block_dev.c:1612
 blkdev_open+0x1cc/0x250 fs/block_dev.c:1770
 do_dentry_open+0x44b/0xec0 fs/open.c:777
 vfs_open+0x105/0x220 fs/open.c:888
 do_last fs/namei.c:3428 [inline]
 path_openat+0xb68/0x2aa0 fs/namei.c:3569
 do_filp_open+0x18e/0x250 fs/namei.c:3603
 do_sys_open+0x292/0x3e0 fs/open.c:1081
 do_syscall_64+0x1d5/0x640 arch/x86/entry/common.c:292
 entry_SYSCALL_64_after_hwframe+0x46/0xbb

The buggy address belongs to the object at ffff88809a001740
 which belongs to the cache kmalloc-2048 of size 2048
The buggy address is located 1416 bytes inside of
 2048-byte region [ffff88809a001740, ffff88809a001f40)
The buggy address belongs to the page:
page:ffffea0002680000 count:1 mapcount:0 mapping:ffff88809a000640 index:0x0 compound_mapcount: 0
flags: 0xfffe0000008100(slab|head)
raw: 00fffe0000008100 ffff88809a000640 0000000000000000 0000000100000003
raw: ffffea000285bfa0 ffffea000230c220 ffff8880aa800c40 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff88809a001b80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88809a001c00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff88809a001c80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                              ^
 ffff88809a001d00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88809a001d80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================
md: invalid raid superblock magic on mtdblock0
md: mtdblock0 does not have a valid v0.0 superblock, not importing!
md: md_import_device returned -22
md: could not open unknown-block(0,0).
md: md_import_device returned -6
md: invalid raid superblock magic on mtdblock0
md: mtdblock0 does not have a valid v0.0 superblock, not importing!
md: md_import_device returned -22
md: could not open unknown-block(0,0).
md: md_import_device returned -6
md: invalid raid superblock magic on mtdblock0
md: mtdblock0 does not have a valid v0.0 superblock, not importing!
md: md_import_device returned -22